U.S. Pat. No. 8,139,816 to French et al. (“the '816 patent”) provides acoustic drivers with stationary and moving coils. Time varying signals are applied to the moving and stationary coils to control the movement of a diaphragm, which produces audible sound. The time varying signals correspond to an input audio signal such that the sound corresponds to the input audio signal. Some of the described embodiments include multiple moving coils, multiple stationary coils or both. Some embodiments include feedback for adjusting one or more of the signals based on a characteristic of the acoustic driver.
U.S. Pat. No. 9,241,213 to French et al. (“the 213 patent”) provides acoustic transducers with stationary and moving coils, and methods for operating the acoustic transducers. Time varying signals are applied to the moving and stationary coils to control the movement of a diaphragm, which produces sound. The time varying signal applied to the moving coil corresponds to at least a processed version of an input audio signal and is updated based on, at least, a version of the time varying signal applied to the stationary coil. Some embodiments include updating the processed version of the input audio signal in response to a magnetic flux value corresponding to the time-varying signal applied to the stationary coil. Some embodiments include updating the time-varying signal applied to the moving coil in response to a feedback signal.